In prior art electrostatic copying processes, a plurality of steps are required for producing a copy of an original document. The first step includes charging a photoconductive surface with a uniform electrostatic charge. The second step comprises exposing the charged photoconductive surface with a light or radiation pattern of the original to form a latent electrostatic image of the copy to be produced. The third step consists of developing the latent electrostatic image with toner powder particles to form a toner powder image in the configuration of the desired copy. Transfer of the toner powder image to a transfer material and fixing or fusing of the transferred image are the fourth and fifth steps in the process. The final step consists of cleaning and discharging the photoconductive surface to remove residual toner particles and discharge residual electrostatic charge in preparation for making another copy.
The prior art performs these steps at various processing stations in which a wide variety of equipment is required to carry out the method. For example, at the exposure station, a light source and optics are needed to illuminate the original, focus the light reflected from the original and provide proper scanning to dissipate charges on the photoconductor, thereby providing a latent image. In addition, a photoconductive surface is needed to produce the copy.
A disadvantage with this prior art process is that with each station expensive equipment is employed, which increases the cost and size of the copying machine. Furthermore, because of the use of a photoconductive surface, the process cannot be performed under ambient lighting conditions. This means that the copying machine must be enclosed or sealed in a manner to prevent ambient light from striking the photoconductor, thereby increasing the complexity and cost of the machine.
In U.S. Pat. No. 2,647,464, an electrostatic photocopying technique is disclosed in which a photoconductor is not used to generate a copy. In this reference the original is placed image side down on a dielectric surface and an electrostatic charge is applied to the surface through the original. Next the original is stripped from the surface, the surface then being developed with toner powder. The powder image is then transferred to a final support material. A disadvantage with this technique is that the latent electrostatic image is disturbed when the original is stripped from the dielectric surface, thereby preventing a clear copy from being produced. Furthermore, a specially prepared dielectric surface made by, for example, vacuum evaporation must be used for this process.